Outcome of adult horses with botulism treated at a veterinary hospital: 92 cases (1989-2013)

Background: There are no studies evaluating a large population of adult horses treated for botulism. Reported survival rates in outbreak situations are low; however, many horses in outbreaks do not receive treatment.

Hypothesis/objectives: That adult horses treated at a veterinary hospital would have improved survival compared to outbreak situations. Additional aims included identification of predictors of nonsurvival.

Animals: All horses greater than 6 months of age with a final diagnosis of botulism admitted to a veterinary teaching hospital between 1989 and 2013 were included.

Methods: Retrospective study. Historical, admission, and hospitalization data were retrieved from medical records and associations between variables and nonsurvival were identified using logistic regression. Two multivariable models were developed pertaining to (1) information available at admission and (2) clinical findings during hospitalization.

Results: Ninety-two records met inclusion criteria. Retained variables for the two models indicated that higher rectal temperature (OR, 1.94; CI, 1.19-3.17) and dysphagia (OR, 4.04; CI, 1.01-16.17) observed at admission increased the odds of survival, as did treatment with antitoxin (OR, 121.30; CI, 9.94-1,480.65). Horses with abnormal respiratory effort or inability to stand had decreased odds of survival. Overall survival was 48% but was significantly higher (67%, P = .011) for horses that arrived standing, and even higher (95%, P < .001) for horses that remained able to stand throughout hospitalization. Complications occurred in 62% of horses but were not associated with nonsurvival.

Conclusions and clinical importance: Horses that lose the ability to stand have a poor chance of survival. Complications are common in treated horses but do not reduce survival.